"We advise people camping to keep away from trees and make sure their tents are on high ground," he said.

"We're also concerned about property damage from fallen trees and branches."

A motorist in Tenterfield was rescued by the SES this morning when their car became trapped in floodwater in a causeway.

Volunteers were able to assist the motorist to safety and retrieve their car, but Mr Campbell says people should avoid driving in flood-affected areas to prevent the situation occurring.

"We have quite a few hundred volunteers on standby, supported by Rural Fire Service, Fire and Rescue NSW, and NSW Police, so we're confident we have the resources we require to respond to any flood situation," he said.

"But we'd like to remind people to avoid driving through floodwaters."

It's a timely reminder, with heavy rain in major river systems in the north.

Flooding confirmed in Darkwood

The Bellinger river, west of Coffs Harbour, was expected to flood this evening, cutting off access to the town of Darkwood late this afternoon.

The flooding was confirmed by SES at 3pm.

Residents were warned well in advance to stock up in case they were isolated, and the SES were keeping a close eye on the rest of the state.

Local Fire Captain Lionel Campbell, who has lived in Darkwood for 24 years, said he had spoken with authorities in Coffs Harbour, and he was prepared to help out if his community was cut off.

"Every time we get a rain event, the low bridges are flooded. We've seen four or five washed away over the years," he said. "If we get a medical emergency, I can radio out, but everyone's pretty well prepared."

The Darkwood region is made up of tight valleys, with homeowners isolated in their own sections.

Mr Campbell said newer residents were prone to panic when they were isolated by water, so they needed to be reassured. He was taking stock of his pantry as the rain drizzled outside.

"In the last 24 hours, we've had about 80 millimetres of rain," Mr Campbell said. "These floods are very inconvenient, but we'll all give each other a hand if it gets much worse."

Heavy winds, rain to hit Sydney on Monday

A spokesperson from the Transport Management Centre said all main roads were currently open, but some were delayed earlier by holiday traffic.

"There's no flooding [on main roads] at the moment, but earlier there were some traffic delays [heading south] coming in to Bulahdelah, where people were packing up and heading back home early because of the rain," the TMC spokesperson said.

The SES have advised motorists to slow down and drive to the conditions.

"Destructive winds and heavy rain will start affecting the Sydney Metro area tomorrow and driving conditions may deteriorate," an SES spokesperson said.

"The safest option could be to travel home tonight or delay the trip for another day."

Cityrail said they had not heard of any of their services being affected as ex-tropical cyclone Oswald moves slowly south.

Relief for Coonabarabran

The rain was inconvenient for some, but it was what residents of Coonabarabran had been praying for.

"We had rainfall on the Coonabarabran fireground last night and early this morning, and we're expecting that to continue for a little while," a Rural Fire Service spokesperson said.

"This has turned the fire into a 'patrol', which means we make sure every log is out and every ember is extinguished."

The ground was too slippery for volunteers to access the fire's remnants.

While rain fell on fires in the north and in the Sydney basin, the RFS said fires in the state's west and on the border of Victoria haven't seen any relief.

"There's five or six weeks of summer left, and while the rain was welcome, we still have a way to go," the RFS spokesperson said.